Traditionally, the performance of a switch has been measured by evaluating its packets forwarding throughput. With the success of Software-Defined Networking (SDN) and its growing number of deployments and applications, however, the requirements for switches are changing. Switches are required to still forward packets as fast as possible, but they also need to support the new dynamic and flexible control plane.
Early SDN deployments already highlighted forwarding table size and its update speed as two critical switches' performance metrics. As the research and industrial communities acquire more and more confidence with the new capabilities introduced with SDN, complex control programs that fully exploits devices' programmability are being increasingly proposed.
This finally adds forwarding table size and its update speed as important performance metrics for tomorrow's switches. Forwarding tables are required to host large numbers of entries, with flexible flow matching patterns, and which undergo frequent updates.
While Ternary Content Addressable Memories (TCAMs) become more and more critical to implement flexible packet matching in hardware, there is still no solution to make them bigger without reducing their speed. The few thousands forwarding entries supported by today's SDN switches are going to be further reduced to enable TCAMs at supporting faster networks. Furthermore, the TCAM entries updating procedures, which potentially require a re-organization of the memory, are proving to be too slow for the upcoming, dynamic network control plane applications.
Modern software switches do not suffer from these issues, since they can perform fast forwarding (wildcard matching) entries installation, but can forward only a few millions of packets per second.